Commonly assigned U.S. Pat. No. 4,603,166 to Poppe et al., issued Jul. 29, 1986, discloses polyphthalamide compositions which, when filled with glass fibers and molded, have heat deflection temperatures at 264 psi, determined according to ASTM D-648, above about 245.degree. C. (473.degree. F.). Included are compositions comprising recurring terephthalamide and adipamide or terephthalamide, isophthalamide and adipamide units and, preferably, wherein the mole ratio of dicarboxylic acid moieties provided by the terephthalamide, isophthalamide and adipamide units is about 65-90:25-0:35-5, respectively. As disclosed therein, such compositions, including particulate- and fiber-filled compositions, exhibit desirable thermal properties including deflection temperature, high tensile strength and flexural modulus and are useful in various applications including preparation of molded articles, fibers, and laminates.
Commonly assigned U.S. Pat. No. 4,617,342 to Poppe et al., issued Oct. 14, 1986, and commonly assigned, copending application Ser. No. 142,469 filed Jan. 8, 1988, and published European Patent Application No. 84300745.1 (Publication No. 0122688), published Oct. 24, 1984, disclose polyphthalamides which, when filled with glass fibers, have heat deflection temperatures at 264 psi, determined according to ASTM D-648, above 240.degree. C. Compositions according to U.S. Pat. No. 4,617,342 are prepared from dicarboxylic acid compounds comprising terephthalic acid and isophthalic acid compounds in a mole ratio of 80:20 to about 99:1 and diamines comprising hexamethylene diamine and trimethylhexamethylene diamine in a mole ratio of about 98:2 to about 60:40. Compositions taught in application Ser. No. 142,469 are based on terephthalic acid and isophthalic acid compounds in a mole ratio of about 70:30 to about 99:1 and hexamethylene diamine. Such compositions have utility in various applications, the neat and fiber-filled compositions being particularly suited for molding applications.
While such poyphthalamides filled with reinforcing fibers can be injection molded into articles having desirable mechanical and thermal properties, injection molding conditions for many of the polyphthalamides, and particularly those having a relatively high content of terephthalamide units (e.g., greater than about 50 mole %) are often more severe than in the case of lower melting point polyamides such as poly(hexamethylene adipamide). Attainment of optimum properties in such polyphthalamide molded articles also can be complicated by molding conditions required to develop sufficient crystallinity in the molded polyphthalamides to achieve significant increases in heat deflection temperature and other properties dependent on crystallinity. In particular, the polyphthalamides have glass transition temperatures ("Tg") generally ranging up to about 130.degree. C.; however conventional steam- or hot water-heated molds, which typically can reach temperatures up to about 100.degree. C. .+-.10.degree. C., may be inadequate to allow for consistent development of sufficient crystallinity in many of the polyphthalamides to obtain significant property appreciation or may require undesirably long molding cycle times to do so. Of course, higher mold temperatures can be achieved with oil heated molds and molding cycle times can be increased or annealing of molded articles can be conducted to increase crystallization and thereby enhance properties dependent thereon; however, these alternatives add cost and complexity to a molding operation. Accordingly, it will be appreciated that it would be desirable to modify such polyphthalamides to facilitate consistent attainment of heat deflection temperatures and other desirable properties in molding without sacrificing other desirable properties.
In general, it is known that modification of polymer properties may be accomplished in various ways. Modification of molecular structure through use of additional or different monomers in polymerization can lead to desirable improvements in some properties. However, the same often are accompanied by loss of other desirable properties and use of additional or different monomers is not always practical due to process considerations. In certain of the above-described polyphthalamides, replacement of terephthalamide units with adipamide units is effective to lower Tg of the compositions, thereby facilitating molding at lower mold temperatures; however, other properties, such as resistance to water absorption and thermal degradation may be sacrificed. Use of additives may lead to property improvements without complicating a polymerization process; however the effects of additives often are unpredictable and, again, improvements in some properties often are achieved at the expense of other properties. For example, addition of plasticizers to the above-described polyphthalamides can result in lowering of Tg but this is achieved at the expense of mechanical properties such as modulus. Blending a given polymer with one or more other polymers may give compositions with a combination of properties intermediate those of the individual components; however, processing requirements often limit the number of candidates that can be blended with a given polymer in an attempt to attain desirable property modifications. Also, blending often is unpredictable; properties of a blend may reflect a desirable balance of the properties of its components or they may be better or worse than those of the components depending on compatibility of the components, reactivity thereof under blending or processing conditions and other factors.
It is an object of this invention to provide fiber-filled polyphthalamide compositions of improved melt processibility. A further object of the invention is to provide such filled compositions capable of being injection molded into articles having desirable mechanical and thermal properties. Another object of the invention is to provide such filled compositions capable of being molded into articles having such properties even when molded using molds heated at below Tg of the polyphthalamide so as to permit use of steam- or hot water-heated molds with a number of such polyphthalamides. Another object of the invention is to provide an improved process for molding such filled polyphthalamide compositions into useful fabricated products. A particular object of the invention is to provide fiber-filled polyphthalamide molding compositions which, when molded using a mold heated to within about 20.degree. C. of Tg of the polyphthalamide, have heat deflection temperatures at 264 psi, according to ASTM D-648, substantially equal to or greater than those achieved when molded using a mold heated at Tg of the polyphthalamide. Other objects of the invention will be apparent to persons skilled in the art from the following description and claims.
I have now found that the objects of this invention can be achieved by providing certain fiber-filled polyphthalamide compositions having at least minor amounts of particulate talc incorporated therein. Such compositions exhibit increases in heat deflection temperature at least comparable to those achieved with the fiber-filled polyphthalamides without particulate talc but at lower mold temperatures. Such improvements are attained using molds heated below Tg of the polyphthalamide component, thereby facilitating use of steam- or hot water-heated molds in molding of some of the polyphthalamides.